How Atwell can help you obtain a Letter of Map Revision (LOMR) and revise flood hazard boundaries on your next development project

By: Jared Gardner, PE, Senior Project Engineer, and Aaron Nichols, PE, Senior Project Engineer

You’ve found the perfect property for your next development project, but there is just one issue: it sits within a floodplain. What are your options?

That’s where we come in with our expertise in the Letter of Map Revision (LOMR) process. A LOMR is a process provided by the Federal Emergency Management Agency (FEMA) that allows for changes to be made to flood hazard maps. As senior project engineers, we’ve worked with clients on numerous projects ranging from 10 to over 600 acres – with watersheds ranging from as little as 10 acres to several square miles – to remove areas from floodplains.

With our team’s detailed research and analysis expertise, developers can see several benefits after going through the LOMR or CLOMR (Conditional Letter of Map Revision) process.


Benefits of a LOMR

Obtaining a LOMR can provide developers with more accurate flood hazard information, increase property value, and offer expanded development opportunities. It allows developers to make more informed decisions and can contribute to more effective and sustainable development practices in flood-prone areas. For a developer, obtaining a LOMR can offer several significant benefits, including:

  • – Expanded development opportunities: If a developer’s land is in a Special Flood Hazard Area (SFHA) according to FEMA’s flood maps, it may have restrictions on development due to floodplain regulations. By obtaining a LOMR and revising the flood hazard boundaries, the developer could potentially expand their development options, allowing for more efficient and larger-scale projects.
  • – Increased property value: Properties in flood-prone areas are often considered less desirable and may have lower market values. Revising flood hazard maps through a LOMR could potentially remove or reduce the flood risk designation, leading to increased property values and potentially attracting more buyers or investors.
  • – Reduced insurance costs: Properties located within SFHAs typically require flood insurance, which can be costly. Revising flood hazard maps through a LOMR could result in the property no longer being designated as high-risk, thereby reducing or eliminating the need for expensive flood insurance coverage.
  • – Streamlined permitting process: Projects located in flood-prone areas often require additional permitting and regulatory approvals. Revising flood hazard maps through a LOMR could streamline the permitting process by reducing the need for specific flood-related requirements, potentially saving time and resources.


How a LOMR helped our client reach their goal

A recent project of ours that benefited from a LOMR was Rancho Mercado in Surprise, Arizona. Rancho Mercado is a single-family residential development, and the site is characterized by desert washes, rocky soil, and native vegetation. The site was almost completely within a floodplain classified as Flood Zone A.

Flood Zone A represents areas with a 1% annual chance of flooding, also commonly referred to as the “base flood” or “100-year flood.” This means that there’s a 1 in 100 chance in any given year that a flood of a particular size will occur in this zone. This translates into a 26% chance of flooding over the life of a 30-year mortgage. Flood Zone A presents challenges because there have been no previous detailed hydraulic analyses to determine base flood elevations (BFEs). In other words, while the risk of flooding is identified, the actual water depth or flood height during a base flood event is typically not provided in these areas.

On the Rancho Mercado project, Atwell worked hand-in-hand with the developer and the local Flood Control District to determine the 1% chance of flood that impacted the site. This particular site was downstream from an unmaintained levee that was graded during World War II to protect a satellite airfield of the Luke Air Force Base. This levee created a significant obstacle as there were multiple locations where the levee had failed.

Our team at Atwell worked with the city of Surprise, the Flood Control District of Maricopa County, and FEMA to derive a plan to manage the flows upstream and downstream of the levee. Not only did this allow Rancho Mercado to develop, but by determining the drainage patterns in the area, we helped open up the door for many other developments to move forward.

Finding the right partner for the LOMR process

It’s important to note that the LOMR process involves a thorough review and analysis by FEMA, and not all requests for map revisions may be approved. Developers considering a LOMR should work closely with qualified experts, such as land use planners, engineers, and hydrologists, to assess the potential benefits and navigate the application process effectively.

If you have questions about your project, we’re always happy to chat. Here is some of our background:

Jared Gardner: Throughout my career, I have specialized in the study of hydraulics and hydrology. I’m a Certified Floodplain Manager (CFM), a licensed Professional Civil Engineer in Arizona and Texas, and I specialize in multiple modeling programs including FLO-2D, HEC-RAS 1D, and HEC-RAS 2D. In the seven years since joining Atwell, I have re-delineated more than 1,400 acres on over 20 separate projects to provide safe and protected developable land. I demonstrate professionalism, extensive knowledge in engineering and hydrology, problem-solving and decision-making skills, and the ability to clearly explain in-depth concepts and principles on every project.

Aaron Nichols: I’m a seasoned water resources engineer with experience in hydrologic and hydraulic modeling, floodplain delineations, and the design of both large and small-scale flood control structures. My hands-on experience with FEMA has given me the expertise to understand and interpret FEMA’s stringent guidelines on any project. I have successfully executed multiple projects utilizing FLO-2D, HEC-RAS 1D, and HEC-RAS 2D software, ultimately receiving approval from FEMA. As a communicator, I bridge the gap between intricate technical nuances and actionable insights.

By choosing the right professional, you can streamline the LOMR process and ensure accurate flood risk assessments for your next development project.

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